Display-device manufacturing method and display device

ABSTRACT

A method for manufacturing a display device includes: a step of forming a first recess, in a planarization film, overlapping a first lower electrode; a step of forming a first lower functional layer in the first recess to have a thickness lower than a depth of the first recess; a step of disposing a first screen, which has an opening corresponding to the first recess, on the planarization film, and coating the first lower functional layer with a first light-emitting layer; a step of sliding a squeegee in contact with the first screen to squeegee the first light-emitting layer and, after the squeegeeing, removing the first screen; and a step of sliding the squeegee in contact with the planarization film to squeegee the first light-emitting layer again.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a displaydevice.

BACKGROUND ART

Patent Document 1 discloses a technique to prepare a cryogenicallycrushed light-emitting-layer material, and to print a light-emittinglayer with the prepared material by electrostatic screen printing.

CITATION LIST Patent Literature

[Patent Document 1] Japanese Unexamined Patent Publication ApplicationNo. 2011-198655

SUMMARY OF INVENTION Technical Problem

A problem of the above technique is that the thickness of the screen isa lower limit of the thickness of the light-emitting layer. Hence, thelight-emitting layer cannot be formed thinner than the screen.

Solution to Problem

A method for manufacturing a display device according to an aspect ofthe present invention includes: a first step of forming a first recessin a planarization film covering a first lower electrode, the firstrecess overlapping the first lower electrode; a second step of forming afirst lower functional layer in the first recess to have a thicknesslower than a depth of the first recess; a third step of disposing afirst screen, which has an opening corresponding to the first recess, onthe planarization film, and coating the first screen and the first lowerfunctional layer with a first light-emitting layer containing quantumdots; a fourth step of sliding a squeegee in contact with the firstscreen to squeegee the first light--emitting layer and, after thesqueegeeing, removing the first screen; and a fifth step of sliding thesqueegee in contact with the planarization film to squeegee the firstlight-emitting layer again.

Advantageous Effect of Invention

An aspect of the present invention makes it possible to form a firstlight-emitting layer thinner than a first screen.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart showing a method for manufacturing a displaydevice according to this embodiment.

FIG. 2(a) to FIG. 2(e) are cross-sectional views illustrating the methodfor manufacturing the display device according to this embodiment.

FIG. 3(a) to FIG. 3(d) are cross-sectional views illustrating the methodfor manufacturing the display device according to this embodiment.

FIG. 4(a) to FIG. 4(e) are cross-sectional views illustrating the methodfor manufacturing the display device according to this embodiment.

FIG. 5(a) to FIG. 5(c) schematically show how dilatancy works.

FIG. 6 is a graph illustrating a relationship between shear rate andviscosity.

FIG. 7(a) is a plan view of the display device according to thisembodiment.

FIG. 7(b) is a cross-sectional view of the display device according tothis embodiment.

FIG. 8 is a flowchart showing a method for manufacturing the displaydevice according to Example 1.

FIG. 9(a) to FIG. 9(f) are cross-sectional views illustrating the methodfor manufacturing the display device according to Example 1.

FIG. 10(a) to FIG. 10(d) are plan views illustrating the method formanufacturing the display device according to Example 1.

FIG. 11(a) and FIG. 11(b) are cross-sectional views of the displaydevice according to Example 1.

FIG. 12(a) to FIG. 12(d) are cross-sectional views illustrating amodification of Example 1.

FIG. 13(a) and FIG. 13(b) are plan views illustrating a method formanufacturing the display device according to Example

DESCRIPTION OF EMBODIMENT

FIG. 1 is a flowchart showing a method for manufacturing a displaydevice according to this embodiment. FIG. 2(a) to FIG. 2(e) arecross-sectional views illustrating the method for manufacturing thedisplay device according to this embodiment. FIG. 3(a) to FIG. 3(d) arecross-sectional views illustrating the method for manufacturing thedisplay device according to this embodiment. FIG. 4(a) to FIG. 4(e) arecross-sectional views illustrating the method for manufacturing thedisplay device according to this embodiment.

In the method for manufacturing the display device according to thisembodiment, a thin-film-transistor layer 2 is formed on a substrate 4 asillustrated in FIG. 2(a). Specifically, on the substrate 4, a controlelectrode CE, an inorganic insulating film 16, a semiconductor layer 12,conductive electrodes Dx and Dy, and an interlayer insulating film 21are formed in the stated order. The control electrode CE functions as agate electrode. The inorganic insulating film 16 functions as a gateinsulating film. One of the conductive electrodes Dx and Dy functions asa source electrode, and the other as a drain electrode.

The substrate 4 can be made of either a glass substrate, or a flexiblebase material containing, as chief component, such a resin as polyimide.The substrate 4 may have an upper face covered with a barrier film (e.g.silicon nitride and silicon oxide) to block such foreign objects aswater and oxygen.

Each of the control electrode CE and the conductive electrodes Dx and Dyis a. monolayer metal film made of at least one of such metals as, forexample, aluminum, tungsten, molybdenum, tantalum, chromium, titanium,and copper. Alternatively, each electrode is a multilayer metal filmmade of these metals. The inorganic insulating film 16 can be either,for example, a silicon oxide film or a silicon nitride film.Alternatively, the inorganic insulating film 16 can be a multilayer filmincluding these films. The semiconductor layer PS is formed of, forexample, oxide semiconductor and low-temperature polysilicon (LIPS). Theinterlayer insulating film 21 is made of such applicable organicmaterials as polyimide, acrylic resin, and epoxy resin. Such materialshave a planarization effect. These resins may be photosensitive.

After that, as illustrated in FIG. 2(b), the interlayer insulating film21 undergoes an ashing process, and the conductive electrodes Dx and Dyare exposed.

At Step S1 of FIG. 1 as illustrated in FIG. 2(c), a metal mask Mf isdisposed in contact with the interlayer insulating film 21, in order toexpose the conductive electrode Dx and shield the conductive electrodeDy. A first lower electrode F1 is formed by such techniques assputtering, vapor deposition, and coating. The first lower electrode F1,which reflects light, is a multilayer stack of, for example, indium tinoxide (ITO) and either silver (Ag) or an alloy containing Ag. The firstlower electrode F1 may be made of such materials as 120, Al, and Mg.After the first lower electrode F1 is deposited, the metal mask Mf isremoved. Note that, instead of disposing the metal mask Mf, a resistpattern may be formed by photolithography.

After that, as illustrated in FIG. 2(d), a planarization film 23 isdeposited to cover the first lower electrode F1. The planarization film23 can be made of, for example, applicable organic materials such aspolyimide, acrylic resin, and epoxy resin. The thickness of theplanarization film 23 on the first lower electrode F1 is equal to thesum of the thicknesses of a first lower functional layer and a firstlight-emitting layer to be described later.

At Step S1 of FIG. 2 as illustrated in FIG. 2(e), the planarization film23 undergoes an ashing process using a metal mask Ms, and a recess H1 isformed to overlap the first lower electrode F1. The ashing process iscarried out until the first lower electrode F1 is exposed. Hence, anedge portion of the first lower electrode F1 is covered with theplanarization film 23, and a non-edge portion of the first lowerelectrode F1 is exposed. In FIG. 2(e), the recess H1 does not overlap achannel portion of the semiconductor layer 12 because planarization isimportant. However, the recess H1 shall not be limited to such aconfiguration. For example, if high definition is requested, the firstlower electrode F1 and the recess H1 may overlap the channel portion ofthe semiconductor layer 12.

At Step S2 of FIG. 1 as illustrated in FIG. 3(a), while the metal maskMs is disposed, a first lower functional layer U1 is formed in the firstrecess H1 to have a thickness lower than a depth Hd of the first recessH1. The first lower functional layer U1 can be formed by such techniquesas sputtering, vapor deposition, and coating.

The first lower functional layer U1 includes at least a carriertransport layer. Examples of materials to form the carrier transportlayer as a hole-transport layer include: such oxides as Cr, Ni, Mg, Mo,W, and La; a H-VI semiconductor compound that is p-type doped or a III-Vsemiconductor compound that is p-type doped; and an inorganic substanceor an organic substance that transports holes. Examples of materials toform the carrier transport layer as an electron-transport layer includeZnO, MgO, ZnMgO, TiO₂, MoO₃, WO₃, and a II-VI semiconductor compoundthat is n-type doped, or a III-V semiconductor compound that is n-typedoped. Note that the electron-transport layer has a thickness ofpreferably 200 nm or less. This is because if the thickness exceeds 200nm, a series resistance component becomes too large to ignore.

The first lower functional layer U1 may include a carrier injectionlayer in addition to the carrier transport layer. A work function of thecarrier injection layer is preferably greater than, or equal to, a workfunction of the first lower electrode F1. The work function (or anionization potential) of the carrier injection layer is smaller than, orequal to, an ionization potential of the carrier transport layer. Such acarrier injection layer allows efficient injection of carriers from thefirst lower electrode F1 into the carrier transport layer. Note that,instead of disposing the metal mask Ms, a resist pattern may be formedby photolithography.

Then, as illustrated in FIG. 3(b), after the first lower electrode F1 isdeposited, the metal mask Ms is removed. A step height between an upperface of the planarization film 23 and an upper face of the first lowerfunctional layer U1 defines a thickness of a first light-emitting layerto be described later. This step height is determined by the depth Hd ofthe first recess H1 and the thickness of the first lower functionallayer U1. The depth Hd of the first recess H1 can be controlled by atime period of the ashing process that the planarization film 23undergoes. The thickness of the first lower functional layer U1 can becontrolled highly precisely by a deposition condition or a depositionrate. if the first lower functional layer U1 is deposited by, forexample, sputtering, a deposition rate of approximately 20 nm/20 min canbe easily achieved. When the deposition rate is controlled by seconds,the thickness of the layer can be controlled on the order of 0.1 nmwithout introducing a special technique.

At Step S3 of FIG. 1 as illustrated in FIG. 3(c) and FIG. 3(d), a firstscreen SC1, which has an opening K1 corresponding to the first recessH1, is disposed in contact with the planarization film 23 so that theopening K1 overlaps the first recess. The first screen SCI and the firstlower functional layer U1 are coated with an ink containing quantum dots(a first light-emitting layer E1 in liquid form). Hence, a remainingportion of the first recess H1 (a portion without the first lowerfunctional layer U1) and the opening K1 are filled with the ink (thefirst light-emitting layer E1 in liquid form).

The opening K1 of the first screen SC11 is sized to preferably containtherein the first recess H1 in plan view. If the opening K1 is as largeas the first recess H1, the ink might be scraped out of the first recessH1 in a squeegeeing process that follows. This problem occurs because,when the squeegee moves, stress concentrates on an end portion of theopening K1 of the first screen SC1. The problem can be solved when theopening K1 where the stress concentrates is separated from the firstrecess H1.

After that, as illustrated in FIG. 4(a), a squeegee SK is slid incontact with the first screen SC1 to squeegee the ink (the firstlight-emitting layer E1). Hence, the ink in the opening of the firstscreen SC 1 stays, while the ink on the top of the first screen isremoved. After the squeegeeing, the first screen SC1 is removed asillustrated in FIG. 4(b).

The ink is made of a solvent in which the quantum dots are dispersed.Thus, when the squeegee SK strokes the first screen SC1, the ink mightbe removed by dilatancy. To prevent the ink from being removed, aparticle volume concentration; that is, a proportion of the total volumeof the quantum dots contained in the ink per unit volume, is desirably45% or less, a viscosity of the ink is preferably 500 Pa·sec or below,and a speed of the stroke is preferably 10 m/sec or slower.

FIG. 5(a) to FIG. 5(c) schematically show how dilatancy works for theink containing quantum dots 31. FIG. 6 is a graph illustrating arelationship between shear rate and ink viscosity. FIG. 5(a) illustratesa state of the ink applied to the screen The ink includes a solvent 32containing the quantum dots 31. When the squeegee strokes the screen,shearing force acts on the ink. Hence, the quantum dots 31 move away,and are immediately spaced apart, from one another. Hence, asillustrated in FIG. 5(b), the increasing space between the quantum dots31 leaves a region 33 creating a negative pressure among the quantumdots 31. Because of the negative pressure among the quantum dots 31, thesolvent 32 around the quantum dots 31 is sucked into the space betweenthe quantum dots 31. Accordingly, the ink loses its fluidity. When theink loses its fluidity and becomes adhesive, the ink forms a lump.Hence, the light-emitting layer is delaminated. As illustrated in FIG. 6a limitation of the dilatancy depends on the ink viscosity, the particlevolume concentration, and the shear rate. As long as the limitation ofthe dilatancy is within the area of the hatching, the delamination ofthe light-emitting layer can be mostly prevented.

Note that a degree of the adhesiveness varies depending on the particlevolume concentration of the ink. The ink is fused with the printingsurface by an anchor effect due to microtexturing on the printingsurface, and by electrostatic adsorption due to the van der Waals force.If the particle volume concentration of the ink is small, the fusionstrength is greater than the adhesiveness.

After that, as illustrated in FIG. 4(c), the squeegee SK is slid incontact with the planarization film 23 to squeegee the firstlight-emitting layer E1 again. Here, a region where no firstlight-emitting layer E1 is found is all flat, and the squeegee canstroke as does so on the screen. Hence, as illustrated in FIG. 4(d), aportion of the first light-emitting layer E1 remains in the first recessH1, and the rest of the first light-emitting layer E1 is removed. Such afeature makes it possible to form the first light-emitting layer E1thinner than the first screen SC1.

After that, as illustrated in FIG. 4(e), a first upper functional layerJ1 and an upper electrode (a common electrode) 25 are formed above thefirst light-emitting layer E1 in the stated order. Hence, alight-emitting element X is formed to include the first lower electrodeF1, the first lower functional layer U1, the first light-emitting layerE1, the first upper functional layer J1, and the upper electrode 25. Theupper electrode 25 is a metal thin film made of, for example, an alloyof magnesium and silver, and is transparent to light.

The light-emitting element X is a quantum-dot light-emitting diode(QLED) including the first light-emitting layer E1 containing quantumdots. Holes and electrons recombine together in the first light-emittinglayer E1 by a drive current between the first lower electrode F1 and theupper electrode 25, which forms an excitors. While the excitorstransforms from the conduction band level to the valence band level ofthe quantum dots, light is released. Note that the first lower electrodeF1 may act as an anode. The upper electrode 25 may act as a cathode. Thefirst lower functional layer U1 may be made of a material at leasttransporting the holes. The first lower electrode F1 may act as acathode. The upper electrode 25 may act as an anode. The first lowerfunctional layer U1 may be made of a material at least transporting the:electrons.

In this embodiment, the depth Hd of the first recess formed in theplanarization film 23 and the film thickness of the first lowerfunctional layer U1 can define the thickness of the first light-emittinglayer E1. Such a feature makes it possible to form the light-emittinglayer thinner than the screen, which has been impossible by screenprinting.

The thickness of the screen is limited by mechanical strength requiredfor printing, materials, and pixel sizes. Hence, the screen cannot be asthin as, or thinner than, approximately 500 μm. Hence, a conventionalscreen printing technique cannot form a light-emitting layer thinnerthan approximately 500 μm. if the light-emitting layer has a thicknessof approximately 500 μm, carriers to be injected are neither uniform norhighly dense across the thickness. Consequently, the light emissionefficiency cannot increase.

Moreover, this embodiment eliminates the need of a vacuuming process tobe used for a conventional light-emitting element manufacturing method.Such a feature can reduce the costs of, and the time for, manufacturinga light-emitting element.

Furthermore, the ink removed by the squeegeeing is recovered and reused.Such a feature makes it possible to use an expensive light-emittingmaterial economically and efficiently. In addition, the surface of thefirst screen SCI is provided with liquid repellent finishing. Such afeature can increase efficiency in recovery of the ink. A technique toprovide the liquid repellent finishing may involve, for example,processing the surface of the first screen SC1 with fluorine to decreasechemical activity. Note that the first screen SC1 can also be reused.

FIG. 7(a) is a plan view of the display device according to thisembodiment. FIG. 7(b) is a cross-sectional view of the display deviceaccording to this embodiment. As illustrated in FIG. 7(a), a displaydevice 10 includes: a display region DA; and a frame region NA. Thedisplay region DA includes a plurality of sub-pixels SP. Each of thesub-pixels includes the light-emitting element X. As illustrated in FIG.7(b), in the sub-pixel SP, the first lower electrode F1 is formed on theinterlayer insulating film 21. In the planarization film 23, the firstrecess H1 is formed to overlap the first lower electrode F1. In thefirst recess H1, the first lower functional layer U1 and the firstlight-emitting layer E1 containing quantum dots are stacked together.The upper face of the planarization film 23 is flush with an upper faceof the first light-emitting layer E1. A state in which a plurality offaces are flush with one another means that the faces continue flatwithout gaps. The state may allow a variation of plus or minus 2 nmbetween the upper face of the planarization film 23 and the position ofthe first light-emitting layer E1. The variation is approximately anaverage radius of the quantum dots contained in the first light-emittinglayer E1.

In plan view, an outer edge of the first lower functional layer U1, anouter edge of the first light-emitting layer E1, and an outer edge ofthe first recess H1 match with one another. The planarization film 23 isan edge cover. A peripheral end portion (an edge) of the first lowerelectrode F1 is covered with the planarization film 23. A non-peripheralend portion of the first lower electrode F1 is in contact with the firstlower functional layer U1.

Formed above the first light-emitting layer E1 are an upper functionallayer 24 and the upper electrode (the common electrode) 25. A sealinglayer 6 is formed to cover the upper electrode 25. The sealing layer 6keeps such foreign objects as water and oxygen from the light-emittingelement X, For example, the sealing layer 6 can include two inorganicsealing films and an organic film formed between the two inorganicsealing films.

In the light-emitting element X, the first lower electrode F1 may be ananode. The upper electrode 25 may be a cathode. The first lowerfunctional layer U1 may at least transport the holes. The first upperfunctional layer J1 may at least transport the electrons.

Moreover, in the light-emitting element X, the first lower electrode F1as the anode, the hole-transport layer, the light-emitting layer, theelectron-transport layer, and the cathode are stacked on top of anotherin the stated order. In another embodiment, however, the stacking orderof the layers shall not be limited to the above order. That is, in thelight-emitting element of another embodiment, the first lower electrodeF1 may be the cathode. The upper electrode 25 may be the anode. Thefirst lower functional layer U1 may at least transport the electrons.The first upper functional layer J1 may at least transport the holes.

EXAMPLE 1

FIG. 8 is a flowchart showing a method for manufacturing the displaydevice according to Example 1. FIG. 9(a) to FIG. 9(f) arecross-sectional views illustrating the method for manufacturing thedisplay device according to Example . FIG. 10(a) to FIG. 10(d) arecross-sectional views illustrating the method for manufacturing thedisplay device according to Example 1. In Example 1, at Step S1 of FIG.8 as illustrated in FIG. 9(a), formed in the thin-film transistor 2 andarranged in an x-direction (in a row direction) are the first lowerelectrode F1, a second lower electrode F2, a third lower electrode F3,and the planarization film 23 covering these lower electrodes. Afterthat, formed in the planarization film 23 are the first recess H1overlapping the first lower electrode F1, a second recess H2 overlappingthe second lower electrode F2, and a third recess H3 overlapping thethird lower electrode F3.

Note that a plurality of the first recesses H1 are arranged in ay-direction (a column direction). A plurality of the second recesses H2are arranged in the y-direction. A plurality of the third recesses H3are arranged in the v-direction. The first recesses H1, the secondrecesses H2, and the third recesses H3 are arranged in the x-direction(the row direction).

At Step S2 of FIG. 8 as illustrated in FIG. 9(b), the first lowerfunctional layer U1 is formed in each first recess H1 to have athickness lower than a depth of the first recess H1. A second lowerfunctional layer U2 is formed in each second recess H2 to have athickness lower than a depth of the second recess H2. A third lowerfunctional layer U3 is formed in each third recess H3 to have athickness lower than a depth of the third recess H3. The first lowerfunctional layer U1, the second lower functional layer U2, and the thirdlower functional layer U3 may be formed of either different materials,or a common material.

At Step S3 of FIG, 8 as illustrated in FIG. 9(c) and FIG. 10(a), thefirst screen SC1, which has the opening K1 to entirely overlap eachfirst recess H1, is disposed in contact with the p1arnarization film 23.The ink (the first light-emitting layer E1 in liquid form) containingquantum dots emitting red light is applied. At Step S4 of FIG. 8 , theink (the first light-emitting layer E1 in liquid form) is squeegeed, andthe first screen SC1 is removed.

At Step S4B of FIG. 8 as illustrated in FIG. 9(d) and FIG. 10(b), asecond screen SC2, which has an opening K2 to entirely overlap eachsecond recess H2, is disposed in contact with the planarization film 23.An ink (a second light-emitting layer E2 in liquid form) containingquantum dots emitting green light is applied. At Step S4C of FIG. 8 ,the ink (the second light-emitting layer E2 in liquid form) issqueegeed, and the second screen SC2 is removed. Here, the second screenSC2 may be the same as the first screen SC1, After Step S4 of FIG. 8 ,the removed first screen SC1 may be reused.

At Step S4D of FIG. 8 as illustrated in FIG. 9(e) and FIG. 10(c), athird screen SC3, which has an opening K3 to entirely overlap each thirdrecess H3, is disposed in contact with the planarization film 23. An ink(a second light-emitting layer E3 in liquid form) containing quantumdots emitting blue light is applied. At Step S4E of FIG. 8 , the ink(the third light-emitting layer E3 in liquid form) is squeegeed, and thethird screen SC3 is removed. Note that a plurality of the firstlight-emitting layers E1 emitting red light are arranged in they-direction (in the column direction). A plurality of the secondlight-emitting layers E2 emitting green light are arranged in they-direction. A plurality of the third light-emitting layers E3 emittingblue light are arranged in the y-direction. The first light-emittinglayers E1, the second light-emitting layers E2, and the thirdlight-emitting layers E3 are arranged in the x-direction.

At Step S5 of FIG. 8 as illustrated in FIG. 9(f) and FIG. 10(d), thesqueegee SK is slid in contact with the planarization film 23 in they-direction (in the column direction in which the light-emitting layersemitting light of the same color are arranged) to squeegee the firstlight-emitting layers E1, the second light-emitting layers E2, and thethird light-emitting layers E3 again. As illustrated in FIG. 10(d), thesqueegee SK is slid preferably in the longitudinal direction of thefirst, the second, and the third recesses.

Example 1 makes it possible to efficiently manufacture the displaydevice including the first light-emitting layers E1 emitting red light,the second light-emitting layers E2 emitting green light, and the firstlight-emitting layers E3 emitting blue light, while the film thicknessesof the light-emitting layers are controlled.

FIG. 11(a) to FIG. 11(d) are cross-sectional views of the display devicemanufactured by the manufacturing method according to Example 1. InExample 1, the upper functional layer 24, the upper electrode 25, andthe sealing layer 6 are formed in common between, and above, the firstlight-emitting layer E1 included in a sub-pixel SP1 and emitting redlight, the second light-emitting layer E2 included in a sub-pixel SP2and emitting green light, and the third light-emitting layer E3 includedin a sub-pixel SP3 and emitting blue light.

Movement of the electrons decreases in the order of the firstlight-emitting layer E1 emitting red light, the second light-emittinglayer E2 emitting green light, and the third light-emitting layer E3emitting blue light. Hence, the thickness of each light-emitting layermay be increased in the stated order, such that distribution of thecarriers can be improved in the thickness direction. That is, the firstlight-emitting layer E1 is formed thicker than the second light-emittinglayer E2, and the second light-emitting layer E2. is formed thicker thanthe third light-emitting layer E3.

As a result, in the display device 10 illustrated in FIG. 11(a),movement of the electrons in the red light-emitting layer E1 decreasesmost. Accordingly, the first lower functional layer 11 is formedpreferably thinner than at least one of the second lower functionallayer U2 or the third lower functional layer U3. Moreover, the firstrecess H1, the second recess H2, and the third recess H3 are formed tohave a uniform depth. The first lower functional layer U1 is formedthinner than the second lower functional layer 1J2. The second lowerfunctional layer U is formed thinner than the third lower functionallayer U3. Thanks to such features, the light-emitting layers are thickerin the order of the first light-emitting layer E1 (e.g. 40 nm), thesecond light-emitting layer E2 (e.g. 30 nm), and the thirdlight-emitting layer E3 (e.g. 20 nm).

In the display device 10 illustrated in FIG. 11(b) according to anotherembodiment, the first recess H1 is formed preferably deeper than atleast one of the second recess H2 or the third recess H3. Moreover, thefirst recess HI is formed preferably deeper than the second recess H2,and the second recess H2 is formed preferably deeper than the thirdrecess H3. Furthermore, the first lower functional layer U1, the secondlower functional layer U2, and the third lower functional layer U3 areformed to have a uniform thickness, Thanks to such a feature, thelight-emitting layers are thicker in the order of the firstlight-emitting layer E1, the second light-emitting layer E2, and thethird light-emitting layer E3.

FIG. 12(a) to FIG. 12(d) are cross-sectional views illustrating amodification of Example 1. In this modification, the first recess H1,the second recess H2 and the third recess H3 are formed linearly in planview (formed to extend in the y-direction), and arranged in thex-direction (in the row direction). In FIG. 12(a), an ink (the firstlight-emitting layer E1 in liquid form) containing red-light-emittingquantum dots is applied, using the first screen SC1 that has the openingK1 to entirely overlap the first recess H1. The applied firstlight-emitting layer E1 is squeegeed. In FIG. 12(b), an ink (the secondlight-emitting layer E2 in liquid form) containing green-light-emittingquantum dots is applied, using the second screen SC2 that has theopening K2 to entirely overlap the second recess H2. The applied secondlight-emitting layer E2 is squeegeed. In FIG. 12(c), an ink (the thirdlight-emitting layer E3 in liquid form) containing blue-light-emittingquantum dots is applied, using the third screen SC3 that has the openingK3 to entirely overlap the third recess H3. The applied thirdlight-emitting layer E3 is squeegeed.

In FIG. 12(d), the squeegee SK is slid in the y-direction (in thedirection to which the light-emitting layers extend) without a screen tosqueegee the first light-emitting layer E1, the second light-emittinglayer E2, and the third light-emitting layer E3 again.

EXAMPLE 2

FIG. 13(a) to FIG. 13(d) are cross-sectional views illustrating a methodfor manufacturing the display device according to Example 2. In Example2, a plurality of the first recesses H1 are formed in a matrix. In FIG.13(a), applied is an ink (the first light-emitting layer E1 in liquidform for emitting white light) containing red-light-emitting quantumdots, green-light-emitting quantum dots, and blue-light-emitting quantumdots, using the first screen SC1 that has the opening K1 to entirelyoverlap each first recess H1. The applied first light-emitting layer E1is squeegeed. In FIG. 13(b), the squeegee SK is slid either in they-direction or in the x-direction without a screen to squeegee the firstlight-emitting layer E1 again. After the squeegeeing in Example 2, ascan he seen in Example 1, the upper functional layer 24 and the upperelectrode 25 are formed, and a color conversion layer emitting light ofone of R, G, and B is provided for each of the sub-pixels. Such featuresmake it possible to present an image with color.

The above embodiments are intended for exemplification and description,and not for limitation, of the present invention. It is apparent forthose skilled in the art that many modifications are available inaccordance with the exemplification and description.

REFERENCE SIGNS LIST

2 Thin-Film-Transistor Layer

4 Substrate

6 Sealing Layer

10 Display Device

12 Semiconductor Layer

16 Inorganic Insulating Film

21 Interlayer Insulating Film

23 Planarization Film

24 Upper Functional Layer

25 Upper E1ectrode

F1 First Lower E1ectrode

U1 First Lower Functional Layer

E1 First Light-Emitting Layer

H1 First Recess

SC1 First Screen

SP Sub-Pixel

X Light-Emitting E1ement

1. A method for manufacturing a display device including a plurality oflight-emitting elements, the method comprising: a first step of forminga first recess in a planarization film covering a first lower electrode,the first recess overlapping the first lower electrode; a second step offorming a first lower functional layer in the first recess to have athickness lower than a depth of the first recess; a third step ofdisposing a first screen, which has an opening corresponding to thefirst recess, on the planarization film, and coating the first screenand the first lower functional layer with a first light-emitting layercontaining quantum dots; a fourth step of sliding a squeegee in contactwith the first screen to squeegee the first light-emitting layer and,after the squeegeeing, removing the first screen; and a fifth step ofsliding the squeegee in contact with the planarization film to squeegeethe first light-emitting layer again.
 2. The method according to claim1, wherein in the fourth step, an upper face of the first screen isflush with an upper face of the first light-emitting layer, and afterthe fifth step, an upper face of the planarization film is flush withthe upper face of the first light-emitting layer.
 3. The methodaccording to claim 1 or 2, wherein a second recess is formed in theplanarization film to overlap a second lower electrode, a second lowerfunctional layer is formed in the second recess to have a thicknesslower than a depth of the second recess, a second screen, which has anopening corresponding to the second recess, is disposed on theplanarization film, the second screen and the second lower functionallayer are coated with a second light-emitting layer containing quantumdots, and the squeegee is slid in contact with the second screen tosqueegee the second light-emitting layer, and, after the squeegeeing,the second screen is removed, and in the fifth step, the firstlight-emitting layer and the second light-emitting layer are squeegeedagain.
 4. The method according to claim 3, wherein a third recess isformed in the planarization film to overlap a third lower electrode, athird lower functional layer is formed in the third recess to have athickness lower than a depth of the third recess, a third screen, whichhas an opening corresponding to the third recess, is disposed on theplanarization film, the third screen and the third lower functionallayer are coated with a third light-emitting layer containing quantumdots, the squeegee is slid in contact with the third screen to squeegeethe third light-emitting layer, and, after the squeegeeing, the thirdscreen is removed, and in the fifth step, the first light-emittinglayer, the second light-emitting layer and the third light-emittinglayer are squeegeed again.
 5. The method according to claim 4, whereineach of the first light-emitting layer, the second light-emitting layer,and the third light-emitting layer emits light in a different color, andthe first recess, the second recess, and the third recess are arrangedin a row direction, and a plurality of first recesses including thefirst recess, a plurality of second recesses including the secondrecess, and a plurality of third recesses including the third recess arearranged in a column direction.
 6. The method according to claim 5,wherein in the fifth step, the squeegee is slid in the column direction.7. The method according to claim 4, wherein each of the firstlight-emitting layer, the second light-emitting layer, and the thirdlight-emitting layer emits light in a different color, each of the firstrecess, the second recess, and the third recess is formed linearly inplan view, and in the fifth step, the squeegee is slid in a longitudinaldirection of the first recess, the second recess, and the third recess.8. The method according to claim 4, wherein the first lower functionallayer, the second lower functional layer, and the third functional layerare formed of a common material.
 9. The method according to claim 4,wherein the first light-emitting layer emits red light, the secondlight-emitting layer emits green light, and the third light-emittinglayer emits blue light.
 10. The method according to claim 9, wherein thefirst lower functional layer is formed thinner than at least one of thesecond lower functional layer or the third lower functional layer. 11.The method according to claim 10, wherein the first lower functionallayer is formed thinner than the second lower functional layer, and thesecond lower functional layer is formed thinner than the third lowerfunctional layer.
 12. The method according to claim 9, wherein the firstrecess is formed deeper than at least one of the second recess or thethird recess.
 13. The method according to claim 12, wherein the firstrecess is formed deeper than the second recess, and the second recess isformed deeper than the third recess. 14-18. (canceled)
 19. A displaydevice including a plurality of light-emitting elements, the displaydevice comprising: a first lower electrode, and a planarization filmformed above the first lower electrode; a first recess formed in theplanarization film, and overlapping the first lower electrode; and afirst lower functional layer and a first light-emitting layer stackedtogether in the first recess, the first light-emitting layer containingquantum dots, wherein an upper face of the planarization film is flushwith an upper face of the first light-emitting layer.
 20. The displaydevice according to claim 19, wherein in plan view, an outer edge of thefirst lower functional layer, an outer edge of the first light-emittinglayer, and an outer edge of the first recess match with one another. 21.The display device according to claim 19, wherein a peripheral endportion of the first lower electrode is covered with the planarizationfilm, and a non-peripheral end portion of the first lower electrode isin contact with the first lower functional layer.
 22. The display deviceaccording to any one of claims 19, further comprising: a second recessand a third recess formed in the planarization film, the second recessoverlapping the second lower electrode, and the third recess overlappingthe third lower electrode; a second lower functional layer and a secondlight-emitting layer stacked together in the second recess, the secondlight-emitting layer containing quantum dots; and a third lowerfunctional layer and a third light-emitting layer stacked together inthe third recess, the third light-emitting layer containing quantumdots, wherein an upper face of the planarization film is flush with anupper face of the second light-emitting layer and an upper face of thethird light-emitting layer.
 23. The display device according to claim22, wherein the first light-emitting layer contains the quantum dotsemitting red light, the second light-emitting layer contains the quantumdots emitting green light, and the third light-emitting layer containsthe quantum dots emitting blue light.
 24. The display device accordingto claim 23, wherein the third recess is shallower than at least one ofthe first recess or the second recess.
 25. The display device accordingto claim 23, wherein the third light-emitting layer is thinner than atleast one of the first light-emitting layer or the second light-emittinglayer. 26-27. (canceled)